The present invention relates to a motor-driven steering lock device for locking steering wheel of a motorcar or the like.
Conventionally, there have been known steering lock devices that are used for locking steering wheel of motorcars or the like for purpose of preventing theft. In a steering lock device, generally, an engagement recess is provided on an outer circumference of a steering shaft that rotates with steering wheel operation. When a lock bolt is advanced into and engaged with the engagement recess, the rotation of the steering shaft is thereby restricted and the steering wheel is locked. When the lock bolt is ejected and disengaged from the engagement recess, on the other hand, the on the rotation of the steering shaft is thereby lifted and the steering wheel is unlocked.
Among the steering lock devices are motor-driven steering lock devices in which an electric motor provides driving force for moving the lock bolt between a locked position where the lock bolt is engaged with the steering shaft and an unlocked position where the lock bolt is disengaged from the steering shaft. In a motor-driven steering lock device disclosed in Japanese Patent Laid-Open Publication No. 2002-205622, a lock bolt moves between a locked position and an unlocked position in synchronization with rotational movement of a cam member actuated by an electric motor. In the motor-driven steering lock device of this type, the cam member is disposed so as to rotate in a direction of the movement of the lock bolt, and there is a problem in that increase in a stroke of the movement of the lock bolt particularly leads to increase in a size of the cam member and thus results in increase in a size of the motor-driven steering lock device itself.
In the motor-driven steering lock devices in which the electric motor provides the driving force for moving the lock bolt between the locked position where the lock bolt is engaged with the steering shaft and the unlocked position where the lock bolt is disengaged from the steering shaft, exertion of a torque on the steering shaft with the lock bolt engaged with the steering shaft may make it impossible to draw out the lock bolt from the engagement recess because a stationary steering torque exerted on the lock bolt brings an inner side surface of the engagement recess into pressure contact with the lock bolt. Increase in a force for drawing out the lock bolt, as a countermeasure against the above problem, requires increase in a size of the electric motor or provision of reduction gears or the like and also causes the problem of the increase in the size of the motor-driven steering lock device. In a motor-driven steering lock device disclosed in Japanese Patent Laid-Open Publication No. 2002-283961, a lock bolt is drawn out from a steering shaft with use of a screw shaft and a nut. The device, however, has a problem in that the drawing operation requires much time because a pitch of a screw thread is small.